Circuit breakers are most commonly used to protect electrical equipment from overload and short circuit events. Large circuit breakers that carry thousands of amps of current are oftentimes installed into metal-enclosed switchgear assemblies, which are also referred to as “switchboards.” Switchgears have large electrical conductors called bus bars (or “buss bars”) that carry current from a power source, such as a power utility, through the circuit breakers, to loads that are protected by the circuit breaker. These large circuit breakers, which can weigh hundreds of pounds, are typically lifted into the switchgear and racked by mounting the circuit breakers into a drawout cradle. A manually controlled or remotely operated mechanism is inserted into the cradle to turn a crank that racks the circuit breaker into the switchgear and completes an electrical circuit which is protected by the breaker.
On the backs of these large circuit breakers facing the rear interior of the switchgear cabinet are connection members, such as bus bars, with pivots (also known as “cluster supports”) that jut out like rails on a train track. Onto these pivots are installed multiple “clusters,” which are electrical connectors that have opposing stacks of plate-like fingers. These fingers straddle the pivots and allow the clusters to adapt their positions to engage bus bar connectors, such as fixed stab terminals (“stabs”) or turnable joint mount (TJM) connectors, which are housed inside the switchgear cabinets during the blind rack-in connection. These fingers are biased by spring elements to stay on the pivots so that the cluster “snaps” onto the pivot. It is important that these clusters remain secured on the pivots because if they become loose or dislodged as the circuit breaker is being racked into the switchgear or during operation of the switchgear, a cross-phase connection or a short circuit from an electrical phase to ground can occur.
The switchgear assembly typically comprises a cabinet that houses a drawout circuit breaker cradle for receiving and supporting the circuit breaker. The drawout cradle simplifies mounting and dismounting of the circuit breaker from field serviceable connections, allowing for ease of installation, removal, and maintenance. At the distal end of the cabinet is a breaker backmold, which is often made from a rigid thermoset material, such as a phenolic resin, and used as a mounting interface. For instance, the backmold attaches to the circuit breaker cradle and provides a mounting surface for current transformers, metering transformers, and the power connectors (e.g., stabs or TJMs). The power connectors are typically designed to engage the circuit breaker clusters, field serviceable connections, and current and metering transformers.
Contemporary TJM power connectors are solid metallic structures with a rectangular base attached via an intermediate yoke to a two-prong forked head, all of which are integrally formed from hot-extrusion metal-working processes. The yoke, which connects the base to the head of the connector, has a solid square-shaped cross-section and operates to carry electrical current from the bus bar to one or more breaker clusters. Current TJM connectors are not designed to provide optimal current density distribution (e.g., electric current per unit area of cross section) when in operation. Current TJM connector designs also fail to mitigate the proximity effect caused by adjacent current-carrying structures. Moreover, existing TJM connectors are not designed to reduce skin effect or maximize thermal convective cooling.